Filter plate, filter plate element, and filter comprising same

ABSTRACT

A filter plate which is longitudinally partitioned between its inlet and outlet ends, and features liquid feed and collection troughs at the respective ends which are of progressively decreasing depth from the medial part of the trough to the extremities thereof. Such plates may be associated in opposed, relatively inverted pairs to form enclosed flow channels characterized by fluid flow rates which are substantially uniform across the full transverse extent of the flow path and which facilitate the utilization of the full areal extent of the filter media employed therewith. Also described in a unitary filter element which may be usefully employed in the filter. 
     The filter of the invention may be highly efficiently employed for dewatering of aqueous biomass suspensions, desalting of proteins, removal of secreted metabolites from cellular suspensions, and the like.

BACKGROUND OF THE INVENTION

1. Field of The Invention

This invention relates generally to cross-flow filters comprising amultiplicity of stacked filter plates, of a type wherein filter elementsare disposed between adjacently paired stacked plates.

2. Description of the Related Art

Stacked plate cross-flow filters are utilized in a variety ofsolids-liquid separation operations, including the dewatering ofsolids-liquid suspensions such as aqueous biomass suspensions, thedesalting of proteins, and the removal of secreted metabolites fromcellular cultures. In such systems, the stacked plates making up thecross-flow filter are typically mounted in a unitary frame structurewhereby the respective plates are retained in alignment, in a so-called"plate and frame" construction. A unitary liquid feed conduit providedwith openings at spaced intervals along its length and extending throughthe stacked plates is typically employed as a feed means from whichinfluent solids-containing liquid is introduced into the flow channelsdefined between adjacent plates in the stacked plate assembly. The flowchannels in the plate and frame filter contain filter elements, such asdisposable filter paper sheets, with which the solids-containing liquidis contacted and through which solids-depleted liquid passes. A unitaryliquid withdrawal conduit featuring openings at spaced intervals alongits length extends through the stacked plates in liquid flowcommunication with the respective flow channels of the stacked plateassembly and conveys solids-depleted liquid out of the filter system.

As filtration proceeds, the filtered solids build up in the flowchannels of the filter, on the "feel liquid sides", i.e., activefiltration surfaces, of the filter sheets. The filter is thenperiodically backwashed, or alternatively, it may be fully shut downafter a predetermined level of solids has accumulated in the flowchannels on the filtration surfaces of the filter sheet elements,following which the system is drained of liquid, and the filter sheetsreplaced as necessary.

In one type of presently marketed stacked filter system, commerciallyavailable from Millipore Corporation (Bedford, Mass.) as the Prostak®cross-flow filter, the adjacent filter plates define a flow channel.Solids-containing influent liquid is fed at one side of the plate from acentral location into a transversely extending feed distributionconduit, which is provided with openings at spaced apart intervals alongthe length of the conduit for egress of the solids-containing liquid. Atthe opposite side of the adjacent plates, the flow channel is similarlyconstructed with a liquid collection conduit having openings along itslength to collect the solids-depleted liquid and discharge same from acentral outlet communicating with the collection conduit.

A major problem which has been encountered in cross-flow filters of theabove-described type is that the liquid flow distribution, as forexample reflected by the volumetric liquid flow rate or liquidsuperficial velocity, is highly non-uniform in the transverse directionsof the flow channel. Such maldistribution of the solids-containingliquid is a result of the fact that the influent liquid is introducedinto the feed distribution conduit at a central location. Due to thepressure drop in the transverse direction, from the medial inlet portout to the extremities of the feed distribution conduit, the locallongitudinal flow (cross-flow of liquid from the inlet side to theoutlet side of the stacked plates, at progressively farther transversedistances from the central liquid inlet port, is progressively reducedto an extent which is commensurate with the pressure drop experienced asthe liquid is directed transversely to the outer extremities of thedistribution conduit. As a result, there is preferential channeling ofthe liquid at the central part of the flow channel from the inlet sideto the outlet side thereof, and concommitant under-utilization of theperipheral areas of the filter. When the solids in the central portionhave been built up to a point requiring backwashing or draining of thefilter, the peripheral areas of the filter still have available capacityto separate solids from the feed liquid.

Such transverse maldistribution of the feed liquid in cross-flow filtersof the aforementioned type could conceivably be overcome by theprovision of header manifolds to introduce feed liquid into thefiltration channels at multiple introduction points along the sides ofthe stacked filter plates, with a corresponding outlet header manifoldarrangement at the opposite side of the stacked plates. Unfortunately,however, such provision would significantly increase the overall systempressure drop as well as the complexity of the filter system, since itcould be necessary to positively seal the multiplicity of feed liquidbranch lines passing from the manifold into the filter.

Another type of stacked plate cross-flow filter which has beencommercialized employs a transversely extending liquid distributionconduit with spaced apart openings therein to introducesolids-containing liquid into the flow channel between adjacent stackedplates, but instead of a central inlet port to flow thesolids-containing liquid to such conduit, the liquid is axially fed intothe conduit from a feed line connected to a transverse extremity of theconduit. Filters of such type are available from Millipore Corporation(Bedford, Mass.) under the trademark Pellicon®. This feed arrangementresults in a progressive diminution of the liquid pressure at increasingtransverse distances from the feed end of the distribution conduit,which in turn results in progressively transversely decreased cross-flowrates of liquid in the flow channel.

In an effort to overcome the aforementioned liquid flow maldistributioncharacteristics of stacked plate filters, filter plates have beenconstructed with baffle elements defining discrete flow channels, withthe intent of achieving a more uniform distribution of thesolids-containing influent liquid across the full areal extent of thefilter elements in the flow channels of the filter.

A filter plate commercially available from Toyo Soda ManufacturingCompany, Ltd. (Tokyo, Japan) features a structure in whichsolids-containing influent liquid is introduced to the flow channel at acentral inlet port at one side of the plate. A wall is disposed in frontof the liquid inlet, extending upwardly from the floor of the flowchannel and transversely toward the extremities of the flow channel, todivide the influent stream into two outwardly directed streams.Downstream from such stream-splitting wall is a longitudinally extendingdivider partition, the stream-splitting wall and the divider partitiontogether forming a "T" construction when viewed in plan view.Longitudinally spaced from and parallel to the stream-splitting wall area series of baffle partitions on either side of the divider partition.The baffles extend transversely part way across the flow channel oneither side of the divider partition, so that there is formed aserpentine flow path for each of the split streams, on the respectivesides of the partition. A unitary liquid outlet port is provided at theopposite side of the stacked plates from the inlet port, whereby therespective serpentine flows are finally joined and discharged from theflow channels of the filter.

Although the dual serpentine flow path arrangement described aboveprovides a somewhat better distribution of liquid flow across the arealextent of the filter paper element, the sharp turns in the flow path atthe extremities of the baffles create edge and entrance effects in theflow streams which produce substantial dead space and bypassing therein.As a result of such anomalous flow phenomena, the filtration efficiencyof the baffled serpentine flow arrangement is significantly reduced.

Accordingly, it would be a substantial advance in the art to provide afilter plate characterized by substantially uniform transversedistribution of liquid from a unitary liquid feed port, and highlyuniform liquid cross-flow across the full transverse extent of the flowchannel formed when plates of such type are stacked to form a cross-flowfilter.

It therefore is an object of the present invention to provide a filterplate of such type, which is simple and efficient in construction andoperation.

It is another object of the invention to provide a cross-flow filtercomprising stacked filter plates of such type.

Other objects and advantages of the invention will be more fullyapparent from the ensuing disclosure and appended claims.

SUMMARY OF THE INVENTION

In a broad aspect, the present invention relates to a filter platesuitable for use with filter sheet elements to form a cross-flow filter.In the filter, pairs of such filter plates are mated with the filtersheet elements therebetween, to form flow channels whereinsolids-containing liquid may be contacted with the filter sheet elementsfor filtration thereof to produce solids-depleted liquid.

The filter plate of the invention has a generally planar and rectangularshape with a substantially flat bottom surface. A top surface of theplate is provided with an upwardly extending wall circumscribinglybounding a flow channel of generally rectangular shape.

A liquid inlet port is disposed at a medial part of a first side of theflow channel, with a liquid outlet port at a medial part of a secondside of the flow channel opposite the first side thereof.

The liquid inlet port is joined in liquid flow communication with aliquid feed trough extending transversely across the first side of theflow channel, and the liquid outlet port is joined in liquid flowcommunication with a liquid collection trough extending transverselyacross the second side of the flow channel.

A plurality of spaced-apart partitions extend upwardly from the floor ofthe flow channel between the liquid feed trough and the liquidcollection trough, such partitions being of lesser height than the wallcircumscribing the flow channel and substantially parallel to oneanother to define a series of sub-channels extending longitudinallybetween the liquid feed trough and the liquid collection trough.

The liquid feed trough in this plate is of progressively decreasingdepth from its medial portion, in communication with the liquid inletport, to its marginal extremities. The liquid collection trough islikewise of progressively decreasing depth from its medial portion, incommunication with the liquid outlet, to its marginal extremities.

Plates of the foregoing type may be utilized in stacked pairs to formenclosed flow channels within which filtration may take place in ahighly efficient manner. Specifically, a first plate of the type broadlydescribed above is paired with a structurally identical second platepositioned in inverted relationship to the first plate such that therespective circumscribingly bounding walls of the first and secondplates are in abutting sealing contact with one another. In such stackedarrangement, a foraminous support of generally rectangular shapeapproximating the dimensions of the flow channel is interposed betweenthe adjacent plates, with filter sheet elements between the foraminoussupport and each of the paired filter plates.

In the operation of such a stacked filter plate assembly, liquidintroduced via the liquid inlet port enters the liquid feed trough andis laterally distributed from the medial portion of the feed trough toits outer extremities. The progessively decreasing cross-section of thecollection trough between the respective plates from the vicinity of theliquid inlet port to the extremities of the trough provides a liquidflow which is longitudinally directed into the sub-channels to provide alongitudinally directed liquid cross-flow which is highly uniform overthe full transverse extent of the flow channel, so that the full arealextent of the sheet filter elements is highly effectively utilized. As aresult, the solids filtration capacity of the stacked plate assembly issubstantially increased and the assembly is capable of significantlyextended operation prior to regeneration of the filter, as compared tothe prior art cross-flow plate and frame filters illustrativelydescribed in the preceding section hereof.

In another aspect, the invention relates to a filter element which maybe usefully employed with filter plates of the typed described above instacked plate filter assemblies. The filter element comprises a supportwhich includes a circumscribing frame with an array of spaced-apart andsubstantially parallelly aligned ribs extending between and joined attheir opposite ends to the frame, so that the ribs and frame form aseries of corresponding substantially parallel filter plate flowchannels.

Openings are provided in the frame in liquid flow communication with thefiltrate flow channels for egress of filtrate from the filtrate flowchannels through the frame openings.

A first filter sheet is continuously secured along its margins to afirst face of the frame, and a second filter sheet is correspondinglycontinuously secured along its margins to a second face of the frame.The first and second filter sheets together with the frame define anenclosed interior volume comprising the filtrate flow channels separatedby the ribs.

In this manner, filtrate entering the enclosed liquid volume of thefilter element through the first and second filter sheets is able toflow in the filtrate flow channels and be discharged from the filterelement through the frame openings which are in liquid flowcommunication with the filtrate flow channels.

Other aspects and features of the invention will be more fully apparentfrom the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a filter plate according to the presentinvention.

FIG. 2 is a sectional elevation view of the filter plate of FIG. 1,taken along line A--A thereof.

FIG. 3 is a sectional elevation view of the filter plate shown in FIG.1, taken along line B--B thereof.

FIG. 4 is a top plan view of a foraminous support suitable for use withpaired plates of the type shown in FIGS. 1-3, to form a stacked platefilter assembly.

FIG. 5 is an edge elevation view of the foraminous support shown in FIG.4.

FIG. 6 is an exploded perspective view of a stacked plate filterassembly according to the present invention, showing the details ofconstruction thereof.

FIG. 7 is a transverse sectional elevation view of a stacked platefilter assembly according to the invention, showing the arrangement ofthe constituent parts thereof.

FIG. 8 is a plan view of a support for a unitary filter element assemblyaccording to the invention.

FIG. 9 is an edge elevation view of a unitary filter element assemblycomprising the support shown in FIG. 8.

FIG. 10 is an exploded perspective view of the filter unitary filterelement assembly shown in FIG. 9, illustrating the arrangement of itsconstituent parts.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

The filter plate of the present invention is adapted to be employed inmultiple pairs to form a stacked plate filter assembly wherein adjacentpaired plates are oriented invertedly with respect to one another, sothata single structured configuration may be employed for all of theplates in the stacked assembly.

The filter plates and the interposed foraminous support employedtherewith may be formed of any suitable materials of construction,including plastics such as polypropylene, polyethylene, polysulfone,polyimides, etc.; ceramics; metals such as stainless steel; andpolymeric fluorocarbons such as polytetrafluoroethylene.

Preferably, the plates and interposed foraminous support are made ofmaterials which are adapted to accommodate high temperatures, so thatthe interior surfaces of the filter may be steam sterilized and/orchemically sanitized for regeneration and reuse.

FIG. 1 shows an illustrative filter plate according to the presentinvention, in plan view. FIG. 2 shows a sectional elevation view of theFIG. 1 plate, taken along line A--A thereof, and FIG. 3 is a sectionalelevation view of the FIG. 1 plate, taken along line B--B thereof.

Referring to these drawings, the plate member 10 is generally planar andmay be rectangular in shape, having a generally square shape in thespecific embodiment shown in FIG. 1. The plate has a substantially flatbottom surface 12 (see FIGS. 2 and 3), and a top surface 14 which issubstantially flat in the peripheral portions of the plate. The topsurface 14 has an upwardly extending wall 16 circumscribingly bounding aflow channel 18 of generally rectangular shape within the bounding wall.

A liquid inlet port 20 is provided at a medial part of a first side 22of the flow channel. A liquid outlet port 24 is correspondingly providedat amedial part of a second side 26 of the flow channel opposite thefirst sidethereof.

The liquid inlet port 20 is joined in liquid flow communication with aliquid feed trough 28 extending transversely across the first side ofthe flow channel. Correspondingly, the liquid outlet port 24 is joinedin liquid flow communication with a liquid collection trough 30extending transversely across the second side of the flow channel.

A plurality of spaced apart partitions 32a, 32b, 32c, 32d, and 32e,extend upwardly from the floor 34 of the flow channel between the liquidfeed trough 28 and the liquid collection trough 30. The partitions32a-32e are of lesser height than the wall 16 circumscribing the flowchannel and are substantially parallel to each other, to define a seriesof sub-channels extending longitudinally between the liquid feed troughand the liquid collection trough.

The liquid feed trough 28 is of progressively decreasing depth from itsmedial portion, in communication with the liquid inlet port, to itsmarginal extremities 36 and 36a.

Likewise, the liquid collection trough 30 is of progressively decreasingdepth from its medial portion, in communication with the liquid outletport, to its marginal extremities 38 and 40. As used in this context,the term "depth" refers to the maximum vertical dimension of the feed orcollection trough as measured from the bottom of the trough to the planeof the floor 34 of the flow channel 18.

Optionally, the plate may feature, as shown in FIG. 1, an interiorcircumscribing wall 42 of lesser height than the circumscribing mainwall 16, to provide a bearing structure for retention of the foraminoussupportshown in FIGS. 4-5 and described more fully hereinafter.

The outer circumscribing wall 16 may as shown be formed with integralcylindrical flanges 44, 46, 48, and 50, each of which circumscribes acircular opening in the periphery of the plate to accommodate thepositioning of the plate on spaced-apart rods, as hereinafter shown inreference to FIG. 6 hereof.

At the medial portions of the first and second sides of the plate, thereare provided respective oblong openings 51 and 52 to accommodate theliquid feed and liquid withdrawal conduits which are employed tointroduceliquid to and remove liquid from the flow channels defined byadjacently paired stacked plates. Such feed and discharge liquidconduits are more fully shown and described with reference to FIG. 6herein. The respective liquid feed and discharge conduits are suitablyformed with spaced-apart perforations therein which permit egress oringress of liquid or out of the flow channel via the above-describedrespective liquid inlet and outlet ports of the plate. In order toassure positive sealing of the flowchannels and adjacently positionedplates relative to the liquid feed and discharge conduits, the liquidinlet and outlet ports of the plate are suitably provided with gasketelements 56 and 58 as shown in FIG. 1, at the bottom surface 12 of theplate.

As an example of plate dimensional characteristics for an illustrativeembodiment of the invention, a filter plate suitable for filtration ofaqueous biomass suspensions may be generally of square shape as shown inFIG. 1 with sides on the order of about 6 inches, and with feed andcollection troughs 28 and 30 which are each 2 millimeters deep at theirmedial portions, continously decreasing to a depth of 1.5 millimeters attheir respective extremities (peripheral portions 36 and 36a of feedtrough 28, and peripheral portions 38 and 40 of collection trough 30).Thetransverse dimensions (width) of each of the sub-channels defined bythe partition walls 32a-e is approximately 2 centimeters.

The details of the plate construction are shown in FIG. 2 with respectto the structural features of the liquid inlet port 20 and liquid outletport24. All structural elements and features are numberedcorrespondingly in FIGS. 2 and 3 with respect to the same systemelements of FIG. 1.

As previously described, the filter plate may be provided with acircumbscribing main wall 16 and an interior circumscribing wall 42 oflesser height than the main wall. Between these respective walls isformeda circumscribing channel (see FIGS. 2 and 3), into which suitableopenings 5 and 6 may communicate as shown in FIGS. 1 and 3. Theserespective openings are usefully employed as filtrate (permeate) flowchannels to convey or drain the solids-depleted filtered liquid or otherpermeate fromthe stacked plate assembly.

Openings 5 and 6 may also be usefully employed as gas flow openings toassist in draining the stacked plate filter upon cessation of normaloperation for regeneration. Thus, when the filter is shut down, gas fromasuitable supply source (not shown) may be introduced in openings 5and/or 6to pressurize the flow channel 18 to a sufficient extent wherethe same canbe drained of accumulated biomass suspension upon thetermination of normalliquid flows through the system.

Similarly, these respective openings could be employed for introductionandegress of steam for steam sterilization of the system or for flowinga chemical sterilant through the flow channel 18 prior to initiation orre-initiation of normal filtration operation.

Further, because the edges of the foraminous support are disposed in thechannel between bounding walls 42 and 16, as shown in FIG. 7, describedmore fully hereinafter, it is also possible to utilize openings 5 and 6asrespective secondary fluid inlet and discharge passages, for flowing asecondary fluid through the foraminous support for mass transfercontacting of the liquid introduced into the flow channel 18 from inletport 20 and discharged from the flow channel in outlet port 24. For suchpurpose, it may be advantageous to symmetrically "block" the channelbetween bounding walls 42 and 16, at symmetrically opposed regions, asshown in FIG. 1, where channel blocking segment 8 is disposed in thechannel along the side thereof containing opening 5, and channelblocking segment 9 is similarly disposed in the channel proximate toopening 6. With such arrangement, fluid entering in opening 5 isdiverted downwardly in the channel as shown in the drawing and acrossthe lower portion of thechannel as shown until it encounters the channelblocking element 9. Subsequently, when the fluid so introduced is issuedfrom the edges of theforaminous support into the opposite portion of thechannel as shown, it flows to outlet opening 6.

Openings 5 and 6 may be appropriately sealed between adjacent plates byprovision of suitable gasket means 3 and 5, respectively, at the flatbottom surface 12 of the plate, as shown in dotted line representationin FIG. 1.

FIGS. 4 and 5 show respective top plan and edge views of an illustrativeforaminous support element for the stacked plate filter assembly.Corresponding features of the plate are shown by the same referencenumerals in these two drawings.

The foraminous support 80 is simply a support element of generallyrectangular shape which is supportively reposable at a first face 82thereof on the partitions 32a-32e and the circumscribing wall 42 of theplate element, with a first filter sheet, e.g. a filter paper sheet,therebetween.

The foraminous support 80 is likewise supportively reposable at a secondface 84 thereof on the partitions and inner bounding wall of acomplementary filter plate paired with the filter plate against whichthe first face 82 of the support is reposed. The second face of theforaminoussupport likewise has a sheet filter element between itssurface and the partitions of the adjacent plate member.

The foraminous support is formed with a plurality of longitudinallyextending interior liquid flow channels 86 and a plurality oftransverselyextending interior liquid flow channels 88, wherein thelongitudinal and transverse channels criss-cross one another toestablish an extended interconnected network for liquid flow through theinterior of the supportelement. Concurrently connecting the internalliquid flow network with the top and bottom foraminous support surfaces84 and 82 on which sheets of filter paper or other filtration sheetmembers are mounted, is an array ofsurface openings 90. Thus, when asheet of filter paper is provided for example on the top surface 84 ofthe foraminous support, the liquid (permeate) component of thesolids-liquid suspension passes through the filter paper and openings 90into the interior liquid flow network comprising channels 86 and 88, forflow through the foraminous support to the edge regions thereof, wherethe solids-depleted liquid filtrate issuesfrom the support into thechannel between bounding walls 16 and 42 and may be removed via openings5 and 6.

FIG. 7 is a transverse sectional elevation view of a stacked platefilter assembly according to the invention, showing the arrangement ofthe constituent parts thereof, and numbered correspondingly to FIGS. 1-5herein. As shown in FIG. 7, the identical complementary upper and lowerplates are mated to one another. To insure positive sealing suitablegaskets (not shown) may be interposed (e.g., in opposing grooves)between the abutting top surfaces of the respective opposed boundingwalls 16. A lower filter sheet 100 is disposed between the lower surface82 of the foraminous support, and the partition bearing surface of thelower filter plate. Likewise, an upper filter sheet 102 is interposedbetween the top surface 84 of the foraminous support and the partitionbearing surfaces ofthe upper filter plate.

By this arrangement, there is formed a series of sub-channels 110, 112,114, 116, 118, and 120 between the filter sheet 102 and the upper filterplate, while correspondingly a series of sub-channels 122, 124, 126,128, 130, and 132 are formed between the filter sheet 100 and the lowerfilter plate, with the sub-channels being longitudinally bounded by theperspective partition walls 32a-32e, as shown.

Although the foraminous support has been shown as a structural elementof mat-like form, the function of the support is merely to positionallyretain the filter sheet on either side thereof and to accommodate theinterior flow of solids-depleted liquid toward the filtrate (permeate)collection means associated with the filter plate.

Accordingly, in lieu of the specific foraminous support structure shown,there may be utilized for the support a conventional wire screenelement, or a sintered metal plate, or any other construction which willprovide the requisite supportive function for the filter sheets andaccommodate flow therebetween toward the liquid permeate collection anddischarge means. For example, the foraminous support may comprise asintered ceramicmaterial, e.g., of alumina, zirconia, etc., having aninternal network of interconnected voids with an average void passagediameter on the order ofabout 1 micron. Such support may have a totalvoid space on the order of from about 50 to about 90% by volume, e.g.,about 80% voids. Further, it is to be recognized that such sinteredceramic plate may be glazed or otherwise treated on selected portions ofits surface to render same liquid impermeable in such regions. Thus, thesintered ceramic plate couldbe selectively glazed to provide for flowthrough the interior thereof of asecond fluid, e.g., a dialysis fluidfor desalting of proteins, amino acids, and/or other biologicalsubstances being contacted with the filter sheets supported on suchsintered plate.

FIG. 6 shows an exploded, perspective view of a stacked plate filteraccording to the present invention, as disposed on a base comprising amounting plate 200 having vertically upwardly extending rods 202, 204,206, and 208 at its respective corner portions, as shown. Mounted on thebase as a lowermost element of the stack, is a filter plate 210 of thetype shown in FIGS. 1-3. The respective rods 202, 206, and 208 extendthrough the circular openings in the plate which are surrounded by therespective cylindrical flanges 212, 216, and 218 (a similar flangedopening, not visible in this view, is provided for rod 204). The liquidfeed conduit 221 for the filter extends through an opening in the baseplate 200 and through the liquid inlet opening 251 of the plate member,sothat when filter plate 210 is in position, the liquid feed opening 253is in register with the liquid inlet opening 251 and liquid inlet port220 ofthe filter plate.

In like manner, the liquid withdrawal conduit 223 extends through acorresponding opening in the base plate 200 and liquid outlet opening252,whereby the liquid discharge opening 257 in conduit 223 is broughtinto register with liquid outlet port 224 when the bottom filter plate210 is properly positioned.

Reposed on the upper bearing surfaces of the partition walls 232 of thebottom filter plate is a filter sheet 300. The filter sheet may be apaperfilter sheet, comprising a non-woven web of cellulosic fibers, orany otherreplaceable or disposable filtration medium commonly providedin sheet formand which is readily cut or otherwise shaped to the formrequired in the filter of the present invention. A particularlyadvantageous filter sheet in filter systems of the type envisioned bythe present invention are polysulfone filter sheets which are readilycommercially available.

Overlying the filter sheet 300 is the foraminous support 302, which isof the form illustratively shown and described with reference to FIGS.4-5 herein. Overlying the foraminous support 302 is filter sheet 306,which may be identical in shape and construction to filter sheet 300.

Overlying the upper filter sheet 306 is a filter plate 310 according tothepresent invention, of identical construction to lower plate 210 butpositionally inverted with respect to the lower plate, to form interiorsub-channels for liquid flow which are configured as shown in FIG. 7when the stacked filter plate assembly of FIG. 6 is fully mated withrespect toits constituent elements.

As shown, the upper filter plate 310 is configured with openings 364 and360 communicating with the circumscribing channel (see FIGS. 2 and 3,showing the channel as disposed between bounding walls 42 and 16)surrounding the main flow channel on the plate. Opening 364 in thisconfiguration is closed by a suitable plug, while opening 360 has afluid introduction passage 362 in flow communication therewith, forfeeding of asecond liquid, e.g., dialysate solution, into thecircumscribing channel (the direction of liquid feeding being indicatedby the arrow P). From thecircumscribing channel, the liquid enters theforaminous support through the edge openings 386 thereof and flowstherethrough to the opposite side of the lower filter plate and into thecircumscribing channel of the lowerplate for discharge through openings368 and 369 and out of the system through the fluid discharge passage369 in the direction indicated by arrow Q. Circumscribing channelopening 366 of the lower filter plate is closed by a suitable plug inthis arrangement.

The stacked filter plate assembly may be retained on the rods 202, 204,206, and 208 by suitable mechanical fasteners, such as washers 312, 314,316, and 318, and respective lock-nuts 320, 322, 324, and 326. For suchpurpose, the rods 202, 204, 206, and 208 are suitably configured withthreaded outer surfaces.

It will be apparent from the foregoing that respective sections ofstacked plates may be variously joined in fluid flow communication withone another in series to form stacked filter "trains" whose constituentsections may be employed to carry out a number of unit operations on aninfluent or feed material, such as concentrating (dewatering), washing,dialyzing, desalting, etc.

For example, a stacked filter train of series-connected sections may beemployed in a cell culturing system of the type disclosed and claimed inmy copending patent application U.S. Ser. No. 06/936,486 filed Nov. 26,1986, the disclosure of which is hereby incorporated by reference, inapplications such as the production in vitro of human immunodeficiencyvirus (HIV) on cellular or synthetic microbead substrates. In such HIVproduction application, a first stacked plate section could be employedtoconcentrate HIV, a second section could be utilized to add media tothe system and a third section could be used to withdraw media from thesystem, all without withdrawing any virus, such as might otherwisepresenta risk of immunosuppressive infection. Thus, a closed systemvirus culturing arrangement is provided, which is highly advantageousnot only for the production of HIV but also the culturing or otherprocessing of pathogenic bacterial, viral, and yeast species.

FIG. 8 is a plan view of a support for a unitary filter element. Thesupport 400 includes a circumscribing frame 402 formed by the respectiveside portions 410, 411, 412, and 413. The circumscribing frame isassociated with an array of spaced-apart and substantially parallellyaligned ribs 414, 415, 416, 417 and 418 extending between and joined attheir opposite ends to the frame (sides 412 and 413, respectively). Theribs and frame thus corporately form a series of correspondingsubstantially parallel filtrate flow channels 420, 422, 424, 426, 428and 430, as shown. Openings 407 are provided in the frame in liquid flowcommunication with the filtrate flow channels for egress of filtratefrom the filtrate flow channels through the frame openings.

FIG. 9 is an edge elevational view of the filter element comprising thesupport shown in FIG. 8. FIG. 10 is an exploded perspective view of theunitary filter element whose edge elevational view is shown in FIG. 9.

As shown in FIGS. 9 and 10, the unitary filter element features a firstfilter sheet 406 which is continuously secured along its margins to afirst face of the frame 402. Likewise, a second filter sheet 400 iscontinuously secured along its margins to a second face of the frame.Whenthus assembled, the first and second filter sheets together with theframe define an enclosed interior volume comprising the filtrate flowchannels separated by the ribs. Accordingly, filtrate entering theenclosed liquid volume through the first and second filter sheets, i.e.,by permeation of liquid through the filter sheets, may flow in thefiltrate flow channels and be discharged from the filter elementsthrough the frame openings 407 which are in liquid communication withthe filtrate flow channels.

The above-described unitary filter element may suitably be constructedand employed for short term filtration operation, e.g., on the order ofabout 6 months, following which the filter element may be discarded andreplacedwith a corresponding new element.

The unitary filter element may be formed of any suitable materials, suchasfor example polysulfone, polyvinylidene fluoride, polypropylene,nitrocellulose, polyethylene, and the like, as may be useful in thedesired end use filtration application. The first and second filtersheetsmay be continuously secured along their margins to the respectivefirst andsecond faces of the frame by any suitable joining or attachmentmethod, including, but not limited to, ultrasonic welding, heat sealing,solvent welding, and adhesive bonding, as well as mechanical affixation.

It will be apparent from the preceding description that any number ofpaired filter plates, with interposed support element and filter sheets,may be assembled to form a cross-flow filter. The number of stackedfilterplates in a specific filter system will be largely determined byspace requirements and constraints, allowable pressure drop in thesystem, solids concentration and volumetric flow rate of the liquid tobe filtered, and the filtration efficiency of the specific filter sheetsemployed.

In a illustrative commercial embodiment having the dimensions for thefilter plates previously described in connection with FIGS. 1-3 hereof,a superficial velocity of aqueous biomass suspension in the range of 1.5meters per second through the flow channel defined between adjacentpairedplates is readily accommodated, at a volumetric feed rate ofapproximately 1 liter of aqueous biomass suspension per minute in theflow channel, without any significant maldistribution of the liquid flowtherein.

With the partitioned sub-channel structure of the flow channel betweenadjacent filter plates in the cross-flow filter of the invention, theinfluent liquid is distributed by the liquid feed trough so thatsubstantially equal amounts of liquid are passed into each of thetransversely spaced-apart sub-channels between adjacent plates. As aresult of the decreasing depth of the liquid feed channel from itsmedial portion to its extremities, the pressure through the collectiontrough is equalized to the extent that the volumetric feedrate of liquidto be filtered is substantially equal in each of the sub-channels.

An analogous construction of the liquid collection trough at theopposite end of the flow channel provides a corresponding uniformcollection of solids-depleted liquid after contacting of thesolids-containing liquid with the filter sheet media.

The filter assembly comprising filter plates of the present invention ishighly hydraulically uniform in operation, without the existence oroperational tendencies toward flow anomalies, such as bypassing,channeling, and "dead space" formations, which are found in stackedplate filters of the prior art. Accordingly, the stacked plate filterassembly of the present invention achieves a substantial advance in theart, which permits the full areal extent of the filter sheet media to beefficiently employed for solids-liquid separation. In consequence,filter assemblies according to the invention are capable of extendedoperation relative to the on-stream operating periods characteristic ofprior art filters, before regeneration or drainage and replacement offilter elements is necessary.

While the invention has been described with reference to specificillustrative embodiments, it will be apparent that there are othervariations, modifications, and embodiments possible within the broadscopeof the invention, and that all such variations, modifications, andembodiments are to be regarded as being within the spirit and scope oftheinvention as hereinafter claimed.

What is claimed is:
 1. A filter element comprising: a support ofgenerally rectangular and planar shape including a generally rectangularand planar circumscribing frame having first and second faces, andcomprising a first pair of opposite side portions joined with a secondpair of opposite side portions forming the frame, with an array ofspaced-apart and substantially parallelly aligned ribs extending betweenand joined at their opposite ends to said first pair of opposite sideportions of said frame, said ribs being substantially parallelly alignedwith said second pair of opposite side portions of the frame, so thatthe ribs and frame form a series of corresponding substantially parallelfiltrate flow channels extending between the first pair of oppositeportions of the frame and substantially parallel to the second pair ofopposite side portions of the frame, and a plurality of filtrate flowpassages extending through said first pair of side portionssubstantially in the plane of said frame and generally parallel to saidribs, each said filtrate flow passage being open at an interior edge ofone of said first pair side portions in liquid flow communication withone of said filtrate flow channels, and being open at an opposite,exterior edge of said one of said first pair side portions to provideexterior edge openings in the first pair of side opposite portions ofsaid frame in liquid flow communication with said filtrate flow channelsfor egress of filtrate from said filtrate flow channels through saidfiltrate flow passages to said frame exterior edge openings;a firstfilter sheet continuously secured along its margin to said first face ofsaid frame; and a second filter sheet continuously secured along itsmargins to said second face of said frame; the first and second filtersheets together with the frame defining an enclosed interior volumecomprising said filtrate flow channels separated by said ribs; wherebyfiltrate entering said enclosed liquid volume through said first andsecond filter sheets may flow in said filtrate flow channels to saidfiltrate flow passages and be discharged from said filter elementthrough said frame exterior edge openings in liquid flow communicationwith said filtrate flow channels.
 2. A filter element according to claim1, wherein the support is formed of a material selected from the groupconsisting of polymers, ceramics, and metals.
 3. A filter elementaccording to claim 1, wherein the support is formed of a polymericmaterial selected from the group consisting of polypropylene,polyethylene, polysulfone, polyimide, and polymeric fluorocarbons.
 4. Afilter element according to claim 1, wherein each said filtrate flowchannel has in liquid flow communication therewith multiple filtrateflow passages.
 5. A filter element according to claim 1, wherein thefilter sheets comprise a non-woven web of cellulosic fibers.
 6. A filterelement according to claim 1, wherein the filter sheets are formed ofpolysulfone.
 7. A filter element support of a type having respectivefaces on which filter sheets are reposed, said support being ofgenerally rectangular and planar shape including a generally rectangularand planar circumscribing frame having first and second faces, andcomprising a first pair of opposite side portions joined with a secondpair of opposite side portions forming the frame, with an array ofspaced-apart and substantially parallelly aligned ribs extending betweenand joined at their opposite ends to said first pair of oppositeportions of said frame, said ribs being substantially parallelly alignedwith said second pair of opposite side portions of the frame, so thatthe ribs and frame form a series of corresponding substantiallyparallelly filtrate flow channels extending between the first pair ofopposite side portions of the frame and substantially parallel to thesecond pair of opposite side portions of the frame, and a plurality offiltrate flow passages extending through said first pair of sideportions substantially in the plane of said frame and generally parallelto said ribs, each said filtrate flow passage being open at an interioredge of one of said first pair side portions in liquid flowcommunication with one of said filtrate flow channels, and being open atan opposite, exterior edge of said one of said first pair side portionsto provide exterior edge openings in the first pair of opposite sideportions of said frame in liquid flow communication with said filtrateflow channels for egress of filtrate from said filtrate flow channelsthrough said filtrate flow passages to said frame exterior edgeopenings.
 8. A filter element support according to claim 7, wherein eachsaid filtrate flow channel has in liquid flow communication therewithmultiple filtrate flow passages.